The Bulgarian government has indicated Marinova's attack was not about her work. Prosecutors said she had been raped, suffocated and beaten with such force that her face was unrecognisable.

The body of 30-year-old Viktoria Marinova was found near the Danube River; it is not known if her death is linked to her work. And Prime Minister Boyko Borissov said Sunday that authorities were working together alongside the "best forensics" team to solve the murder.

Bulgarian interior minister Mladen Marinov initially denied that Marinova's murder was linked to her reporting, and said there was no evidence she had been threatened.

"In certain countries there is just not enough enforcement of the law", Robert Mahoney, deputy executive director of the Committee to Protect Journalists, told NPR.

Mahoney says that it is too early to say whether Marinova's killing falls into that category.

Bulgarian police have detained a suspect in connection with the killing of investigative journalist Viktoria Marinova, whose body was found in a park in her hometown of Ruse four days ago, a government source familiar with the investigation told Reuters on Tuesday.

Through a United Nations spokesperson, Secretary-General António Guterres called on "all governments to strengthen press freedom and ensure there is accountability for crimes committed against journalists".

Marinova's killing was widely-condemned on Twitter by fellow journalists and watchdog groups.

An unnamed suspect, only described as a "Romanian citizen with a passport from Moldova", had been arrested in Marinova's murder, according to the national radio report.

"Viktoria's death, the brutal manner in which she was killed, is an execution", Yordanov said.

Marinova is at least the third journalist to have suffered a violent death in the European Union alone over the past 12 months, after Jan Kuciak in Slovakia in February and Daphne Caruana Galizia in Malta in October previous year.

In what would be her final show to air, Marinova addressed the constraints of practicing journalism in her country.

But Bivol.bg owner Asen Yordanov said he had received credible information his journalists were in danger of being assaulted because of the investigation that featured on Ms Marinova's show.